The present invention relates to the field of aircraft surveillance and monitoring, particularly toward a technique known as Automatic Dependent Surveillance.
The Automatic Dependent Surveillance-Broadcast (ADS-B) concept has been introduced as a means to enhance future ground and avionics based surveillance of aircraft. This concept is defined in Minimum Aviation System Performance Standards for Automatic Dependent Surveillance Broadcast (ADS-B), RTCA/DO-186, February 1998, which is later referred to as ADS-B MASPS and is incorporated herein by reference. The ADS-B concept provides for aircraft and ground vehicles to periodically broadcast their state vector (horizontal and vertical position, horizontal and vertical velocity) and other information.
A specific implementation of a 1090 MHz based ADS-B system is described in Drouilhet et al., U.S. Pat. No. 5,570,095, issued Oct. 29, 1996 and incorporated herein by reference. The broadcast ADS-B message provides surveillance information to other users, principally Air Traffic Control (ATC) and aircraft/vehicle operators.
Applications for ADS-B include ATC display of traffic, runway incursion detection and alerting, and Cockpit Display of Traffic Information (CDTI). One example of CDTI is a map-like display centered on a pilot""s aircraft showing relative positions and intentions of other proximate aircraft. Another example of CDTI is provided in Buchanan et al., U.S. Pat. No. 4,196,474, issued Apr. 1, 1980, also incorporated herein by reference.
The Federal Aviation Administration (FAA) and the National Aeronautics and Space Administration (NASA) have investigated the suitability of this technology to support these applications in the airport surface environment. NASA recently tested ADS-B using 1090 MHz data transmission in an airport surface environment as part of the Low Visibility Landing and Surface Operations (LVLASO) program. Tests have been performed to assess how well 1090 MHz ADS-B performs with respect to surveillance system requirements established by the International Civil Aviation Organization (ICAO) and RTCA.
Two issues were identified during ADS-B system implementation and testing at Atlanta Hartsfield International Airport (ATL) as described in xe2x80x9cApplication of ADS-B for Airport Surface Surveillancexe2x80x9d, Dan Hicok, Derrick Lee, 17th Digital Avionics System Conference, November, 1998:
1. A method may be required for CDTI equipped aircraft to obtain surveillance information on aircraft and ground vehicles which are not equipped with ADS-B.
2. Loss of ADS-B surveillance may occur due to multipath, blockage, and antenna pattern nulls.
Aircraft equipped with ADS-B and CDTI receive surveillance information directly from ADS-B transmissions. ADS-B implementation may require installation of new avionics equipment. There may inevitably be a transition period when some aircraft are ADS-B equipped and other aircraft are not. ADS-B MASPS has defined a means to augment ADS-B with a Traffic Information Services (TIS) data link, whereby ground based surveillance information for all aircraft is transmitted to CDTI capable aircraft.
An example of a TIS implementation may be found in Crow, U.S. Pat. No. 5,627,546, issued May 6, 1997, and incorporated herein by reference. Two sources of TIS traffic information are secondary surveillance radar and multilateration, as described in Schwab, U.S. Pat. No. 5,528,244, issued Jun. 18, 1996, and Alsup et al., U.S. Pat. No. 5,191,342, issued Mar. 3, 1993, both of which are incorporated herein by reference. A TIS data link was implemented at ATL for testing. A major limitation of TIS is the implementation may require aircraft owners to purchase a second data link in addition to the ADS-B link.
ATL testing also showed obstructions and multipath from structures may result in degradation or total loss of direct aircraft-to-aircraft ADS-B surveillance. The airport surface environment may be particularly challenging due to the presence of large structures, such as concourses and hangars. Loss of surveillance and degraded surveillance negatively impacts the ability of a pilot to maintain situational awareness of arrivals, departures and runway occupancy.
Accordingly, what is needed is a new method to augment the ADS-B concept using the ADS-B data link to provide surveillance information for aircraft and ground vehicles which are not equipped with ADS-B. This new method needs to provide a means to reinforce ADS-B transmissions which are adversely impacted by the environment.
The present invention provides an improved apparatus and method for use with Automatic Dependent Surveillance-Broadcast (ADS-B). In a method and apparatus of the present invention, each ADS-B equipped aircraft may periodically broadcast its position as derived from its navigation system.
Aircraft with ADS-B receivers may then be able to receive these broadcasts to obtain the location of proximate ADS-B equipped aircraft. The invention provides a means to augment ADS-B transmissions with position and identification information of aircraft which may not be ADS-B equipped.
In addition, the present invention reinforces ADS-B transmissions in areas where line-of-sight or multipath issues prevent reliable ADS-B communications between two aircraft.